1. Field of the Invention
The present invention generally relates to a recording method and apparatus using a liquid printing device. More particularly, the present invention is directed to a transfer-type recording mechanism in which a liquid printing device prints a recording liquid on a layer of an intermediate transfer element provided on an intermediate transfer medium in response to an imaging signal to form an image on the layer of the intermediate transfer element, and then the image is transferred to a recording medium.
2. Description of the Related Art
A recording method using an ink jet recording device, in which a recording liquid containing a color agent, usually referred to as ink, is emitted as a droplet under control of an image signal representative of information to be printed as so to achieve recording of an image, is advantageous in that a structure of the ink jet recording device is comparatively simple and that a noise generated by its recording operation can be reduced to an almost negligible amount. However, printing quality problems associated with producing images directly on a recording medium using ink jet technology include variations in printing conditions and quality depending on a type of a recording medium, such as an overhead projector sheet, a synthetic paper, an ink jet-dedicated paper or other recording media. In addition, when printing on plain paper with a typical water-soluble ink, deterioration of printing resolution occurs because of ink liquid blur and ink liquid penetration problems (i.e., the ink liquid penetrates through the plain paper to a back surface of the plain paper) due to ink liquid migration through paper fibers. Further, there is another problem that a printed image which is not dried fully is degraded when the recorded medium is ejected from a recording apparatus.
A recording method designed to solve the above-mentioned problems is described in U.S. Pat. Nos. 4,528,156 and 5,099,256. This method is a so-called intermediate transfer method in which, first an ink image is produced on an intermediate transfer medium via an ink jet recorder, and then the ink image on the intermediate transfer medium is transferred from the transfer medium to a recording medium. Such an intermediate transfer method includes a significant feature that a recording head is arranged at a predetermined spacing between the recording head and the recording medium so as to prevent clogging of the recording head caused by contamination due to paper fragments and dust. However, when an ink liquid is printed on the transfer medium, the ink liquid spreads inadequately, flows and mixes when producing a multicolor image, thereby producing an inaccurate image. This phenomenon is herein referred to as “ink liquid crawling.”
In order to solve the above problems, Japanese Laid-Open Patent Application No. 62-92849 describes a transfer method in which, first an ink liquid is printed on an intermediate transfer medium, a large portion of a water content of the ink liquid formed thereon is evaporated to produce a condensed ink liquid, which is in turn transferred to a recording medium. This method has an advantageous affect that a vivid image can be obtained, but is not applicable to a high-speed recording, energy-saving and high-resolution recording system because frequently, thermal energies and devices are required for generating the condensed ink on the transfer medium.
Japanese Laid-Open Patent Application No. 3-55283 teaches another method based on the intermediate transfer method, in which an ejected ink provided on an ink transfer medium is cooled partially so as to solidify the ink and to achieve a recording. A local cooling of the ejected ink induces a formation of high viscosity of the ink which can be transferred to a recording medium.
Japanese Laid-Open Patent Application No. 5-200999 describes another method in which an ink liquid is printed on a transfer drum which includes a water-absorptive layer on its surface. A water content of the ink liquid is absorbed by the water-absorptive layer due to its high absorption ability so as to form a condensed ink thereon, and then it is transferred to a recording medium. An advantage of this method is that a vivid image formation can be accomplished, because only the condensed ink formed on the water-absorptive layer by absorbing water contained in the ink liquid can be transferred to the recording medium.
Like Japanese Laid-Open Patent Application No. 62-92849, the above two methods are not suitable for high-speed printing, the energy-saving and the high resolution printing system as well as a compact and a light apparatus, because of the same reasons described with respect to Japanese Laid-Open Patent Application No 62-92849.
Japanese Laid-Open Patent Application No. 7-89067 discloses another method based on an ink jet recording method, which permits a transfer efficiency and image formation to be improved. An ink droplet is discharged on an intermediate transfer layer having a surface carrying a surfactant for improving wetability to form an image thereon, which is in turn transferred to a recording medium. In general, a typical surface active agent has an inherent property that reduces surface tension of a solution. When a water-based ink droplet used in the ink jet recording method is discharged on such a layer, it is natural that reduction of surface tension between the ink droplet and the above layer occurs, thereby causing spreading of the ink droplet thereon. In other words, there is a disadvantage in that it is difficult to obtain a high resolution image with good sharpness because an overall dimension of the ink liquid is likely to spread on the layer coated by the surfactant in comparison with an ink liquid size ejected from a recording head. Moreover, since the ink liquid is transferred to a recording medium together with the surface active agent, an additional disadvantage is that ink liquid bleeding occurs due to co-penetration of the ink liquid and the surface active agent into the recording medium, such as a paper.
Japanese Laid-Open Patent Application No. 7-145576 describes a specialized ink with which a printing quality is independent of the type of a recording medium, and a transfer medium from which only an image part is separated. Because transfer based on this type is carried out at temperature of from about 200° C. to about 300° C. as a softening temperature of a separating layer, there is provided a problem of d high-speed recording and system reliability.
Japanese Laid-Open Patent Application No. 10-58664 discloses still another method in which an ink liquid containing a dye having a quaternary ammonium salt in the side chain is printed on an anionic ion-exchange resin layer on the uppermost layer of an intermediate transfer medium using an ink jet generator, and the ink liquid is modified through chemical action during transportation of the transfer medium and transferred to a recording medium. This method provides an advantage that a transfer efficiency can be improved. On the other hand, this method has a drawback in that, because of ion-exchangeable modification of a dye composition in the ink liquid with the ion-exchange resin layer, a color tone of the ink on the recording medium is changed subtly. Generally speaking, since the ion-exchange resin layer functions such that only an ion can be exchanged with another one and does not absorb water contained in ink liquids, the only dye composition of the ink liquid printed on the ion-exchange resin layer is subjected to chemical modification. Because a concentration of the ink liquid remains constant, the ink is transferred to the recording medium, thereby producing a problem that a transferred image experiences ink liquid blurring, penetration problems and color mixing. In addition, since an ammonia gas is generated upon heating the ion-exchange resin layer for reuse, there is provided a pollution problem. Additionally, this method does not meet the requirement for a high-speed printing, low energy consumption, high resolution printing, compact and light system with maintenance-free operation due to deterioration and reuse and the like for the ion-exchange resin layer.
Japanese Laid-Open Patent Application No. 11-188858 by the present applicant discloses a recording method and apparatus which use an intermediate transfer medium having a powder layer which is removably provided on the transfer medium to receive a liquid from a printing head. In this recording method, the liquid is emitted in response to an image signal to produce an image on the intermediate transfer medium, and then the image thereon is transferred to a recording medium. The powder layer is formed of a polymer powder with high water-absorbing ability, and is dissolvable and swellable by the liquid and causes an increase in viscosity of the liquid residing thereon prior to transfer to a final recording medium. However, this has a problem that there are required a dedicated cleaning members, such as a blade and a brush or the like for cleaning the unused powder remaining on the intermediate transfer medium after transfer to the recording medium.
In general, since an area of a background portion of the intermediate transfer medium is larger than that of an imaged part, a quantity of the powder for use in this type tends to become large. Additionally, when the powder in an unused state is allowed to stand for a long time, the powder on the intermediate transfer medium absorbs water to cause viscosity of the powder to be increased, thereby leading to occurrence of a problem that the powder having water absorbed can not be cleaned by the cleaning member.
Moreover, properties such as water resistance and light resistance for a dye-based ink liquid is usually inferior to that for a pigment-based ink liquid, although images formed by the former have high chroma and vivid color tones. Japanese Laid-Open Patent Application No. 54-68303 describes an ink liquid containing an aqueous organic ultraviolet stabilizer. However, this ink liquid causes a clogged recording head problem and another disadvantage in that ejection stability is unsatisfactory for the ink jet recording method in which the ink droplet is ejected.
The foregoing patents solve some problems associated with the ink jet recording which produces images on the recording medium, but the major problems of image feathering, color to color blur and liquid penetration have not been solved.